This investigation deals broadly with the chemical behaviors of purines and pyrimidines in nucleic acids under the influence of electromagnetic radiations, mutagens and carcinogens. We plan to study chemical reactions which may cause base transitions, transversions and their equivalents. The objectives are to search for molecular bases of carcinogenesis and mutagenesis, to establish the structure-biological activity relationship of carcinogens, and to search for potential cancer chemotherapeutic agents.